Endometrial atypical (bizarre) stromal cells: a potential diagnostic pitfall in biopsy.

Atypical stromal cells (ASCs) may be detected in endometrial polyps and, more rarely, in normal endometrium. Owing to their worrisome cytological features, these cells may represent a potential diagnostic pitfall and are often misinterpreted as malignant, particularly in biopsy samples. We report on ASCs in proliferative phase endometrium of a woman who underwent biopsy for vaginal bleeding. Morphological and immunohistochemical features are discussed in detail. The differential diagnosis to endometrial malignant tumors containing atypical mesenchymal cells is provided.